Safe Speed Forums

It seems that a frequently cited justification for a reduced speed limit, particularly in villages, is "to assist crossing pedestrians". The implied (sometimes explicit) assumption is that pedestrians will necessarily find it easier to cross a major road safely if traffic is travelling slower rather than faster.

This might appear intuitively self-evident but, except to a limited extent, I'm not all sure that it's true. Particularly, I don't think it's at all true to assert that reducing the speed of traffic will necessarily make crossing a road easier. I think, in some cases, there's a strong probability it will make things worse. My reasoning is as follows.

In order to cross a road safely, what one needs (as a pedestrian), is a gap in traffic sufficient to allow the road to be crossed (without undue haste) with reasonable safety margin. At a guess, an 'active' person needs at least a 3-4 seconds gap (depending on the width of the road of course). An elderly person or less confident person may need much more - perhaps 6 seconds or more. Within reasonable bounds (say 20mph - 50mph), I don't think the actual traffic speed is too important - x seconds is x seconds regardless of speed, and the minimum gap (defined by time) doesn't change.

If that premise is accepted, then it follows that in order to assist crossing pedestrians, we must identify the traffic conditions that will be more rather than less likely to generate a "sufficient gap". It appears to me that a speed limit which is set below the 'natural' speed for a road will tend to cause traffic to bunch up (meaning the gaps will be tend to be smaller with less likelihood of a larger gap developing). On the other hand, free flowing traffic will include vehicles whose drivers will have a range of different 'natural' speeds, and this will allow (intermittent) larger gaps to develop. This will make crossing easier even if the overall mean speed of the vehicles is higher.

I'm not suggesting speed limits in villages should be removed - just that the intuitive assumption that "slower traffic = easier crossing" does not apply in the real world. Any comments?

I totally agree with you.

That reasoning is spot on and doesn't just apply to pedestrians. The A140 had a blanket 50mph imposed which is well below the 'natural' speed in most places. Turning right onto it is now a pain because you get long lines of traffic from each direction. At peak times I have timed a wait of over three minutes (just me, not in a queue) before there was a gap to allow the turn.

The counter-arguement is that if the pedestrian misjudges his crossing he will be hit by a faster moving vehicle.

I used to walk to work, and have to cross two roads along the way -- one had a 30 mph limit with speed cameras, and the other had a 40 mph limit with no cameras.

What I found was that on the 40 mph road it didn't take long for a break in the traffic to appear in both directions, when I could cross safely.

On the 30 mph road, on the other hand, it was pretty much a constant steady stream of traffic to the point where I sometimes had to just risk it and run across the road between cars. Not too fun, I can assure you.

I dislike drivers going too slowly when I want to cross, but then I also wouldn't want to cross a dual carriageway where if i fell over on the road they might not be able to stop in time.

Is 30mph the happy medium?

Not on dual carriageways.

Absolutely agree.

Orange mentions the comparison between two different roads, I used to be able to do that comparison at one spot. My walk to work used to see me crossing a 30 s/c where a camera overlooked the crossing point in one direction, leaving traffic in the other direction free to cruise along at 35-40 (not just guessing here, I also used to drive along that stretch...). Crossing the lane overseen by the camera was almost always a lesson in patience, crossing the lane full of nasty horrid speeder-boo hiss-was almost never such a lesson. The volume of traffic was pretty much identical in both directions, the only clear difference was in the speeds...

And similarly to Semitone, I now routinely end up waiting for 2-3 minutes for a gap to open up (or for a driver to be kind and deliberately make one for me) on the 30 s/c I need to get onto every day - if the traffic isn't light enough to allow it to free-flow at (again) 35-40, the resultant nose to tail procession simply doesn't offer any chances for a non-kamikaze move out of the side roads.

So yes, forcing traffic to bunch up at a lower speed than it'd be travelling given free choice of speeds, does make life difficult for other road users, especially if none of those drivers stuck in an artificially slowed-down train of vehicles is in a particularly giving mood-and I find the more a driver is forced into altering their natural behaviour, the less giving they seem to become...

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Chris

That's rather oversimplifying things.

Faster traffic will have bigger gaps which will give the drivers a better view of the road ahead and more time to react.

Also, pedestrians are less likely to take risks if they don't think traffic can stop so quickly.

Very interesting this, and I agree with the original post.

Applying a "traffic orientated" spin in it, consider trying to turn right at a T-junction. In a 20 zone, it's more than likely that you will never see an adequate gap in the traffic flow to merge into. More often than not, you'll be invited in by a driver in the queue.

In a 40 zone, I suspect that finding an adequate gap to merge in to would be easier.

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Simon

I'd also argue that on medium - high speed roads where there are crossings provided, reduction in limits encourages pedestrians to cross anywhere other than the crossings, I can think of a few places near me that end up with dead pedestrians on a regular basis when there are perfectly safe crossings (lights or footbridge), but pedestrians decide to take a chance. Other factors may also come into play??

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